1. Field of the Invention
The present invention relates to an apparatus used for preventing an image blur generated by, e.g., a hand vibration.
2. Related Background Art
In the field of camera apparatuses such as video cameras, still cameras, and the like, in recent years, size and weight reductions are remarkable, and at the same time, multi-functions are attained. As one of multi-functions, an increase in zoom ratio of the photographing lens is an example. For example, zoom lenses with zoom ratios of .times.10, .times.12, and the like are normally used in home-use cameras.
However, as the focal length at the telephoto side assumes a larger value as the zoom ratio increases, the influence of a hand vibration on a recorded image increases. For example, in a dynamic image of a video camera, a principal object image unnaturally moves in a frame; in a still image, a blurred image is undesirably recorded. In a still image, such a problem can be avoided to some extent by increasing, e.g., the shutter speed. However, since dynamic image recording is time-base recording, the influence of a hand vibration cannot naturally be avoided by appropriately setting the shutter speed. In this situation, mainly in the field of video cameras, an image blur (vibration) prevention apparatus for eliminating the influence of a hand vibration has been put into practical applications.
The vibration prevention apparatus includes at least vibration detection means for detecting a vibration (image blur) component, and vibration correction means for correcting the vibration in accordance with the detection result of the detection means. Of these means, the vibration detection means adopts, e.g., a so-called electronic detection method for comparing images in two continuous frames, or a method of directly measuring the actual motion of a camera using an angular velocimeter, an angular accelerometer, or the like.
On the other hand, the vibration correction means adopts a so-called electronic correction method for electronically selecting a range to be actually recorded (extraction range) from an obtained image, or comprises optical vibration correction means for optically adjusting the angle of the photographing optical axis in a direction to remove any hand vibration.
Of the optical vibration correction means, a system using a variable apex angle prism will be described below with reference to FIGS. 19A to 23.
FIGS. 19A to 19C show the arrangement of a variable apex angle prism. Referring to FIGS. 19A, 19B, and 19C, glass plates 21 and 23 and a bellows portion 27 consisting of, e.g., polyethylene define a space in which a transparent liquid such as silicone oil is sealed.
In FIG. 19B, the two glass plates 21 and 23 are parallel to each other, and in this case, the incident and exit angles of light rays of the variable apex angle prism are equal to each other. On the other hand, when the two glass plates 21 and 23 define a certain angle therebetween, as shown in FIG. 19A or 19C, light rays 24 or 26 are deflected through a given angle.
Therefore, when a camera is inclined due to a cause such as a hand vibration, the angle of the variable apex angle prism arranged in front of a lens is controlled to deflect light rays through an angle corresponding to the inclination angle of the camera, thereby removing the vibration.
FIGS. 20A and 20B show this state. Assuming that the variable apex angle prism is in a parallel state and the photographing optical axis matches the center of an object in FIG. 20A, the variable apex angle prism is driven in correspondence with a vibration of a.degree., as shown in FIG. 20B, so as to deflect light rays. As a result, the photographing optical axis continues to match the center of the object.
FIG. 21 shows an actual arrangement of a variable apex angle prism unit, which includes the variable apex angle prism, an actuator portion for driving the prism, and an apex sensor for detecting the angle state.
Since an actual vibration may appear in any direction, the front and rear glass plates of the variable apex angle prism are respectively rotatable about rotation axes having a 90.degree. difference. Note that suffices a and b respectively correspond to constituting members in these two rotation directions, and members denoted by the same reference numerals have the same functions. Some b-side members are not shown.
A variable apex angle prism main body 41 is constituted by the glass plates 21 and 23, the bellows portion 27, and a liquid filled therein. The glass plates are integrally attached to holding frames 28 (28a and 28b) using, e.g., an adhesive. The holding frames 28 constitute rotation axes 33 (33a and 33b) together with stationary members (not shown), and are pivotal about these axes. The axes 33a and 33b extend in directions having a 90.degree. difference. A coil 35 (35a or 35b) is integrally arranged on each holding frame 28, and a magnet 36 (36a or 36b) and yokes 37 (37a or 37b) and 38 (38a or 38b) are arranged on a stationary portion (not shown). Therefore, when a current is supplied to each coil, the variable apex angle prism is pivoted about the corresponding axis 33. A slit 29 (29a or 29b) is formed at the distal end portion of an arm portion 30 (30a or 30b) integrally extending from each holding frame 28, and constitutes an apex sensor together with a light-emitting element 31 (31a or 31b) such as an iRED element arranged on a stationary portion, and a light-receiving element such as a PSD.
FIG. 22 is a block diagram of an image blur prevention lens system as a combination of a lens and a vibration prevention apparatus which comprises the variable apex angle prism as vibration correction means.
Referring to FIG. 22, the system comprises a variable apex angle prism 41, apex sensors 43 and 44, detection circuit units (amplification circuits) 53 and 54 for amplifying the outputs from the apex sensors, a microcomputer (.mu.-com) 45, vibration detection means 46 and 47 comprising, e.g., angular accelerometers, actuators 48 and 49 constituted by the above-mentioned members (from the coils 35 to the yokes 38), and a lens 52.
The microcomputer 45 determines currents to be supplied to the actuators 48 and 49 in correspondence with the angle states detected by the apex sensors 43 and 44 and the detection results of the vibration detection means 46 and 47, so as to control the variable apex angle prism in an optimal angle state for removing a vibration.
Note that principal components are divided into two blocks since control operations are independently executed in directions having a 90.degree. difference.
FIG. 23 shows the detailed structure of a conventional variable apex angle prism. Referring to FIG. 23, the prism comprises the glass plates 21 and 23, the bellows portion 27, a liquid sealed in a space defined by the glass plates and the bellows portion, and an optical axis 25. The bellows portion 27 is formed by coupling four doughnut-shaped films 59 to 62 via coupling portions 57, and coupling these films to frame members 55 via coupling portions 58. Each frame member 55 has a frame core member 56.
Of these members, the coupling portion 57 between each two adjacent films is formed by fusion. For this reason, each of the films 59 to 62 preferably has two surface layers consisting of a material which can provide good heat seal performance. For example, each surface layer normally consists of polyethylene (PE), polypropylene (PP), or the like. Each frame member 55 is fixed to the glass plate 21 or 23 using an adhesive. On the other hand, the coupling portion between each frame member 55 and the film 59 or 62 constituting the bellows must consist of the same material as the film surface if fusion is used in coupling as in the coupling portion 57. However, the above-mentioned material which can provide good heat seal performance can hardly provide high parts precision as compared to, e.g., polycarbonate (PC) popularly used in such a lens barrel. In addition, the above-mentioned material easily deforms due to low rigidity. Therefore, the frame core member 56 is used to avoid these problems. The frame core member 56 consists of a plastic material or a metal such as aluminum, stainless steel, or the like, which has a higher rigidity and a higher thermal deformation temperature than those of the material of the frame member 55. With reference to this frame core member 56, the frame member 55 is formed around the frame core member 56 by, e.g., insert molding. In this manner, a sufficient flatness of a portion, to which a film is fused, of the frame member 55, a sufficient mechanical strength or dimensional precision of a portion for supporting the glass plate 21 or 23, and a sufficient dimensional precision of the fitting diameter of the glass are obtained.
The arrangement using the variable apex angle prism as optical vibration correction means has been described.
A method of movably arranging a correction optical system disclosed in, e.g., U.S. Pat. No. 2,959,088, as another example of the optical vibration correction means, will be described below.
FIG. 24 shows the arrangement of the overall correction optical system.
Referring to FIG. 24, lenses 71 and 72 constitute a correction optical system for main lenses 82 and 83. The focal lengths of these lenses of the correction optical system are set as follows. Let f.sub.1 be the focal length of the lens 71 fixed to a lens barrel 74 and having a negative power, and f.sub.2 be the focal length of the lens 72 supported by a movable support portion 73 and having a positive power. Then, the focal lengths of these lenses are set to satisfy: EQU f.sub.1 =-f.sub.2
Furthermore, the lens 72 is supported by a gimbal 75 to be rotatable about two axes.
A counterweight 80 is arranged to balance the correction optical system.
When such an optical condition is satisfied, a vibration prevention apparatus including a so-called inertia pendulum type optical vibration correction means is realized.
Biaxial movement of the gimbal 75 will be explained below with reference to FIG. 25.
The lens 72 is supported by a support member 75y which has a degree of freedom in the y-direction, and the support member 75y is supported by a support member 75x which has a degree of freedom in the x-direction perpendicular to the y-direction. Furthermore, the support member 75x is supported by the lens barrel 74.
With this arrangement, the correction optical system which has a degree of freedom in two axes is realized.
A typical zoom lens system upon combination of the above-mentioned vibration correction means with the variable apex angle prism and a zoom lens will be described below. In the following description, a so-called inner or rear focus type zoom lens system which attains focusing using a lens group behind a variator lens group for zooming will be exemplified.
Various arrangements of such lens systems are known. In this case, FIG. 26 shows an example of an arrangement which uses the rearmost lens group for focusing. Referring to FIG. 26, the lens system comprises a stationary front-element lens group 111, a variator lens group 112, a stationary lens group 113, and a focusing (compensator) lens group 114. The lens system also comprises an anti-rotation guide rod 133, a variator feed rod 134, a stationary lens barrel 135, an aperture unit 136 (inserted in a direction perpendicular to the plane of the drawing of FIG. 26), a stepping motor 137 as a focus motor, and an output shaft 138 of the stepping motor. A male screw portion is formed on the output shaft 138 to move the lens. A female screw portion 139 meshes with this male screw portion, and is integrated with a movable frame 140 of the lens group 114. The lens system further comprises guide rods 141 and 142 for the movable frame of the lens group 141, a rear plate 143 for fixing the guide rods in an aligned state, and a relay holder 144. The lens system also comprises a zoom motor 145, a deceleration unit 146 for the zoom motor, and interlocking gears 147 and 148. The gear 148 is fixed to the variator feed rod 134.
In the above arrangement, when the stepping motor 137 is driven, the focus lens group 114 moves in the optical axis direction by a screw feed operation. When the zoom motor 145 is driven, the variator lens group 112 moves in the optical axis direction upon rotation of the shaft 134 by means of the interlocking gears 147 and 148.
FIG. 27 shows the positional relationship between the variator and focus lens groups in the above-mentioned lens system in correspondence with some distances. FIG. 27 exemplifies the in-focus positional relationships corresponding to object distances of infinity, 2 m, 1 m, 80 cm, and 0 cm. In the case of the inner focus zoom lens system, since the positional relationship between the variator and focus lens groups varies depending on the object distance, the lens groups cannot be interlocked by a simple mechanism unlike a cam ring of a front-element focus lens.
Therefore, an out-of-focus state occurs if the zoom motor 145 is simply driven in the structure shown in FIG. 26.
The above-mentioned characteristics have delayed practical applications of the inner focus lens system although the inner focus lens system has advantages, i.e., "good closest-distance photographing performance", "small number of constituting lenses", and the like.
However, in recent years, a technique for optimally controlling the lens positional relationship shown in FIG. 27 in correspondence with the object distance has been developed, and products adopting the technique are commercially available.
For example, Japanese Laid-Open Patent Application Nos. 1-280709, 1-321416, and 2-144509 by the same applicant as the present invention proposed a method of tracing the locus of the positional relationship between two lenses in correspondence with the distance.
In Japanese Laid-Open Patent Application No. 1-280709 by the present applicant, the positional relationship between the variator and the compensator (focus lens) is maintained by a method shown in FIGS. 28 to 30.
FIG. 28 is a block diagram of this system. Lens groups 111 to 114 are the same as those shown in FIG. 26. The position of the variator lens group 112 is detected by a zoom encoder 149. The encoder may comprise, e.g., a volume encoder in which a brush integrally attached to a variator moving ring slides along a board with a printed resistor pattern. An aperture encoder 150 uses an output from a Hall element arranged in, e.g., an aperture meter. An image pickup element 151 such as a CCD is connected to a camera signal processing circuit 152. A Y signal output from the camera processing circuit 152 is supplied to an AF circuit 153. The AF circuit discriminates an in-focus or defocus state, and also discriminates a near- or far-focus state and the defocus amount in the case of the defocus state. These discrimination results are supplied to a CPU 154.
A power-ON reset circuit 155 performs various reset operations upon power-ON. A zoom operation circuit 156 supplies the operation contents of a zoom switch 157 by an operator to the CPU 154. A memory stores locus data shown in FIG. 27, i.e., direction data 158, velocity data 159, and boundary data 160. A zoom motor driver 161 and a stepping motor driver 162 are connected to the CPU 154. The number of input pulses to the stepping motor is continuously counted by the CPU, and is used as an encoder of the absolute position of the focus lens. In this arrangement, since the variator position and the focus lens position are respectively obtained by the zoom encoder 149 and the number of input pulses to the stepping motor, a point on the map shown in FIG. 27 is determined. On the other hand, the map shown in FIG. 27 is divided by the boundary data 160 into small strip-like regions, as shown in FIG. 29. In FIG. 29, hatched portions correspond to regions where the lens is inhibited from being located. When one point on the map is determined, one of the small regions, to which the point belongs, can be determined.
As the velocity and direction data, the rotational speeds and directions of the stepping motor, which are obtained based on the locus passing the centers of the regions, are stored in units of regions. For example, in FIG. 29, the abscissa is divided into 10 zones. Assuming that the zoom time is 10 sec, the passing time per zone is 1 sec. FIG. 30 is an enlarged view of block III in FIG. 29. In this block, a locus 164 passes the center, a locus 165 passes the lower left corner, and a locus 166 passes the upper right corner. The central locus can be traced without generating any error when the lens moves at a velocity of x mm/sec.
If the velocity obtained as described above is called a region representative velocity, values corresponding to the respective regions are stored in a velocity memory in correspondence with the number of small regions. If this velocity is represented by 168, the representative velocity is finely adjusted like 167 or 169 on the basis of the detection result of an automatic focus adjustment device, thereby setting the velocity of the stepping motor. On the other hand, since the rotation direction of the stepping motor changes even upon zooming from the telephoto side to the wide-angle side (or vice versa), the sign of the direction is stored as the direction data.
The region representative velocity obtained based on the variator and focus lens positions is corrected on the basis of the detection result of an automatic focus detection circuit to determine a stepping motor velocity. The stepping motor is driven using the determined stepping motor velocity during the zoom driving operation to control the focus lens position. Thus, an out-of-focus state can be prevented even during the zoom operation in the inner focus lens system.
Note that a method in which velocities 167 and 169 are stored in the memory in addition to the representative velocity 168 in FIG. 30, and one of these three different velocities is selected in correspondence with the detection result of the automatic focus detection device is proposed by Japanese Laid-Open Patent Application No. 2-173605 by the present applicant.
In addition to the method of storing the velocities, the following method is known. In this method, some curves corresponding to object distances of .infin., 2 m, 1 m, and the like shown in FIG. 27 are stored in a memory as the focus lens positions corresponding to a plurality of variator positions. When the distance corresponds to an intermediate distance between two stored curves, the positional relationship between the two lens groups is calculated by interpolating data of the upper and lower stored curves.
FIG. 31 shows an arrangement used when the vibration correction means using the variable apex angle prism is coupled to the above-mentioned zoom lens.
Referring to FIG. 31, a rotation shaft 263 is formed integrally with each holding frame 28. A rotation shaft 267 is arranged at the opposite side to the rotation shaft 263, and is not formed integrally with the holding frame 28 in terms of assembling but is constituted by fitting, e.g., a metal shaft (e.g., stainless steel) into the holding frame under pressure. A leaf spring 268 is fixed by a screw 269. A flat glass plate 266 is arranged to avoid, e.g., a photographer from directly touching and damaging the variable apex angle prism. An attachment screw 265 for an accessory is formed near the glass plate 266. A stationary lens barrel part 264 includes holes for receiving the rotation shaft of the variable apex angle prism.
This lens barrel part 264 is fastened to a stationary lens barrel 135 of the zoom lens by a screw 270.
In FIG. 31, the holding frame for pivoting the front glass plate of the variable apex angle prism, actuators, apex sensors, and the like are not shown for the sake of simplicity.
However, when the above-mentioned optical vibration correction means which uses the variable apex angle prism or the movable correction optical system is used, a color shift due to the influence of chromatic aberration, which is generated in principle upon deflection of the optical axis, stands out especially when the correction angle is large, if the focal length of the combined zoom lens is large, or if a portion of a frame is to be recorded in an enlarged scale by, e.g., electronic zooming.
This problem is suppressed to a negligible level in the conventional apparatus. However, a conventionally negligible chromatic aberration level may contribute to a deterioration factor of image quality in consideration of the following future backgrounds: image quality is improving due to an increase in the number of pixels of a CCD as an image sensor, the above-mentioned electronic enlargement function (so-called electronic zooming) is becoming a standard function, a camera with improved image quality such as 3-CCD camera is becoming commercially available, and so on.